<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>全屏上中下布局</title>
  <link rel="stylesheet" href="css/common.css">
  <link rel="stylesheet" href="css/fb01.css">
</head>

<body>

  <div class="flex-box">
    <div>上<br>上2</div>
    <div>中</div>
    <div>下</div>
  </div>


</body>

</html>